Although silicon solar cells have seen impressive progress in recent years, there are inherent limitations in their performance and cost due to the material’s properties. Perovskite technology can overcome these limitations, but so far it has performed below its full potential. Our latest study identifies a major reason for this and points the way forward.explains Ted Sargent, University of Toronto
The perovskite tandem solar cell designed by Sargent and colleagues provides extremely high efficiency and standard voltage. In the prototype version, the scientists demonstrated potential that could, in theory, circumvent basic limitations of conventional silicon solar cells. As if the advantages were not enough, we have another advantage: the new technology should ensure lower production costs.
While commonly used solar cells are made of wafers of very pure silicon, perovskite cells are made of nanocrystals. They can be dispersed in a liquid and then applied to the surface using inexpensive and readily available techniques. As a result, the final cost has become much lower. In addition, by adjusting the thickness and chemical composition of the crystalline layers, these devices can be tuned to absorb specific wavelengths of light and convert them into electricity. In contrast, silicon always absorbs the same part of the solar spectrum.
The authors write about the details of their research in the pages nature. As they show, they used two different layers of perovskite, each tuned to a different part of the solar spectrum. This is how the tandem solar cell was born. The top layer has a wider bandgap that absorbs well the ultraviolet part of the spectrum as well as some visible light. The lower one has a narrow gap and is tuned to the infrared part of the spectrum. This provides greater flexibility than silicone cells.
Perovskite tandem solar cells provide high efficiency and conversion efficiency
Interestingly, the key innovation was implemented when the researchers analyzed the interface between the perovskite layer, where light is absorbed and converted into excited electrons, and the adjacent layer, which is called the electron transport layer. As it turned out, the electric field at the surface of the perovskite layer was not uniform.
In the prototype version, the solar cell measures one square centimeter and produces an open-circuit voltage of 2.19 eV, which is a record for all perovskite tandem solar cells. The energy conversion efficiency reached 27.4%, which is higher than the current record. At the time of independent accreditation by the National Renewable Energy Laboratory, efficiency was measured at 26.3%. Moreover, the new cell maintained 86% of its initial efficiency after 500 hours of continuous operation.
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